1. Field of the Invention
The present invention relates in general to contact image sensor modules in facsimiles or personal computers for reading characters and pictures on documents, and more particularly to a contact image sensor module of high quality which is capable of perfectly removing a cross-over between metal lines which is unavoidable in a matrix circuit wiring manner.
2. Description of the Prior Art
Generally, a contact image sensor is a device which is used to sense a character or a picture on a document in transmission and reception of the document content in a facsimile. The performance of the contact image sensor is dependent on the signal process time an accurate signal with no noise therefrom can be outputted.
A linear contact image sensor of the matrix circuit wiring manner is comprised of thin film devices which have recently developed concentratedly to act up to an information age. With the linear contact image sensor of the matrix circuit wiring manner, data can be read out by only one read-out IC and the production of a compact system is enabled, resulting in reduction in the manufacturing cost of the sensor and increase in the yield thereof.
Referring to FIG. 1, there is shown a circuit diagram of a conventional linear contact image sensor of a parallel read-out manner which has conventionally been employed most frequently. The reference numeral UC designates a unit cell which is comprised of a photodiode PD as optical sensing means for receiving light being incident upon from a document to produce a photocharge and a thin film transistor (TFT) TR as switching means for passing the photocharge produced from the photodiode PD. The reference numeral Ci in the unit cell UC designates an internal capacitance in the photodiode PD which is shown in the form of an equivalent circuit.
As shown in FIG. 1, the linear contact image sensor of the parallel read-out manner comprises a plurality of blocks BL1-BLn which are arranged successively and linearly. Each of the blocks BL1-BLn has m unit cells UC1-UCm. Each of a plurality of gate address lines GAL1-GALn is connected in common to gate terminals of m TFTs TR1-TRm in the m unit cells UC1-UCm in a corresponding one of the plurality of blocks BL1-BLn to apply a bias from a driving circuit DC to the corresponding block. Each of a plurality of data lines DL1-DLm is connected to a drain terminal of a corresponding one of the TFTs TR1-TRm in the m unit cells UC1-UCm in every the block to transmit data simultaneously outputted from the corresponding block to a reading-out circuit RC.
In operation, the photodiodes PD of the plurality of unit cells UC1,1-UCn,m in the plurality of blocks BL1-BLn receive the light being incident upon from the document and produce the resultant photocharges. At this time, the gate bias from the driving circuit DC is applied to a corresponding one of the plurality of blocks BL1-BLn via a corresponding one of the plurality of gate address lines GAL1-GALn. For example, provided that the gate bias from the driving circuit DC is applied to the ith block BLi, the m unit cells UCi,1-UCi,m in the ith block BLi are simultaneously addressed. As a result, m data are outputted in parallel from the ith block BLi. The m data from the ith block BLi are transmitted through the m data lines DL1-DLm to the reading-out circuit RC, which then processes the data transmitted through the data lines DL1-DLm.
In FIG. 1, a photodiode reverse bias V.sub.PD is shown to be applied simultaneously to the n blocks BL1-BLn through a single photodiode reverse bias application line PBL. Since the photodiodes PD1,1-PDn,m of the plurality of unit cells UC1,1-UCn,m in the plurality of blocks BL1-BLn all are applied with the reverse bias V.sub.PD, the photodiodes PD1,1-PDn,m produce the photocharges according to the intensity of the light being incident upon from the document and output pure photocurrent resulting from the produced photocharges.
However, the conventional linear contact image sensor of the parallel read-out manner has a disadvantage, in that cross-overs (portions a in FIG. 1) between the adjacent data lines DL are formed, resulting in formation of parasitic capacitances. The parasitic capacitances causes crosstalks and leaks between the data lines resulting in generation of a distortion and a noise in the data signal. As a result, the data become inaccurate. Also, cross-overs (portions b in FIG. 1) between the adjacent gate address and data lines GAL and DL are formed, resulting in formation of parasitic capacitances. The parasitic capacitances absorb a portion of the date signal charges being transmitted through the data lines to the reading-out circuit, thereby causing the output data to become inaccurate. Furthermore, in order to discharge the absorbed charges and then transmit the discharged charges to the reading-out circuit RC, there may be required a constant charge transfer time after the turning-off of the gate bias. This results in an unnecessary increase in the data read-out time.
Referring to FIG. 2, there is shown a circuit diagram of a conventional linear contact image sensor of a selective read-out manner. The linear contact image sensor of the selective read-out manner in FIG. 2 is a sensor for an improvement in the linear contact image sensor of the parallel read-out manner. Herein, a unit cell UC is comprised of a light sensing photodiode PD and a switching thin film transistor (TFT) TR.
As shown in FIG. 2, the linear contact image sensor of the selective read-out manner comprises a plurality of blocks BL1-BLm which are arranged successively and linearly. Each of the blocks BL1-BLm has n unit cells UC1-UCn. The linear contact image sensor of the selective read-out manner also comprises n gate address lines GAL1-GALn corresponding to the n unit cells UC1-UCn in every the block and m data lines DL1-DLm corresponding to the blocks BL1-BLm.
Namely, each of the n gate address lines GAL1-GALn is connected to a gate terminal of a corresponding one of the TFTs TR1-TRn in the n unit cells UC1-UCn in every the block and each of the data lines DL1-DLm is connected in common to drain terminals of the n TFTs TR1-TRn in the n unit cells UC1-UCn in a corresponding one of the plurality of blocks BL1-BLm.
In operation, the photodiodes PD1,1-PDm,n of the plurality of unit cells UC1,1-UCm,n in the plurality of blocks BLt-BLm receive the light being incident upon from the document and produce the resultant photocharges. At this time, the driving circuit DC selects one of the plurality of gate address lines GAL1-GALn, thereby to turn on a corresponding one of the TFTs TR1-TRn in the n unit cells UC1-UCn in every the block. As a result, data is outputted from the unit cell in every the block corresponding to the selected gate address line. Namely, one data is selectively outputted in the unit of the block and the data selectively outputted from the blocks are applied through the corresponding data lines DL1-DLm, respectively, to the reading-out Circuit RC.
In FIG. 2, similarly to that shown in FIG. 1, a photodiode reverse bias V.sub.PD is shown to be applied simultaneously to the photodiodes PD1,1-PDm,n of the plurality of unit cells UC1,1-UCm,n in the m blocks BL1-BLm through a single photodiode reverse bias application line PBL.
In the linear contact image sensor of FIG. 2, for example, the data are outputted from the ith unit cells UC1,i-UCn,i in the blocks BL1-BLm corresponding to the selected gate address line GAL1 and the output data are transmitted through the corresponding data lines, respectively. As a result, the cross-overs a between the adjacent data lines DL as shown in FIG. 1 are not formed, resulting in no formation of parasitic capacitances.
However, in the linear contact image sensor of FIG. 2, similarly to that in FIG. 1, there are still present the parasitic capacitances due to the cross-overs (portions c in FIG. 2) between the adjacent data and gate address lines DL and GAL. This results in generation of a noise in the data signal and, thus, an unnecessary increase in the data read-out time.
On the other hand, in the linear contact image sensor of FIG. 2, differently from that in FIG. 1, there may be formed parasitic capacitances due to cross-overs (portions d in FIG. 2) between the adjacent gate address lines GAL. These parasitic capacitances are of no direct relevance to the data lines DL and thus have no effect on the data signal so far as a short fail is not generated.
Referring to FIG. 3, there is shown a circuit diagram of a conventional linear contact image sensor of a meander line manner. As shown in this figure, each of m unit cells UC1-UCm is comprised of a photodiode PD and a thin film transistor (TFT) TR. Gate terminals of the TFTs TR1-TRm in the m unit cells UC1-UCm are connected in common to a gate address line GAL, which is connected in the unit of block. As a result, the total 38 address lines GAL1-GAL38 are provided to simultaneously address the m unit cells UC1-UCm in the unit of block BL. One of the m unit cells UC1-UC38,m in the 38 blocks BL1-BL38 is selected in the unit of block and drain terminals of the TFTs TR of the 38 unit cells UC thus selected are connected in common, thereby to form a data line DL.
It the linear contact image sensor of the meander line manner in FIG. 3, the drain terminals of the TFTs in the unit cells arranged at the same position in the unit of two blocks are connected to each other, thereby to form a data line of the meander structure. For example, the data lines of the meander structure may be formed as follows: the first data line DL1 is formed by connecting, in consecutive order, the drain terminal of the TFT TR1,1 of the first unit cell UC1,1 in the first block BL1, the drain terminal of the TFT TR2,m of the mth unit cell UC2,m in the second block BL2, . . . , the drain terminal of the TFT TR37,1 of the first unit cell UC37,1 in the 37th block BL1 and the drain terminal of the TFT TR38,m of the mth unit cell UC38,m in the 38th block BL38.
On the other hand, m data lines DL1-DLm are connected to the drain terminals of the TFTs TR1,1-TR38,m of the m unit cells UC1,1-UC38,m in the 38 blocks BL1-BL38, respectively. For example, in the first block BL1, the first unit cell UC1,1 is connected to the first data line DL1, the second unit cell UC1,2 is connected to the second data line DL2, . . . , the m-1th unit cell UC1,m-1 is connected to the m-1th data line DLm-1 and the mth unit cell UC1,m is connected to the mth data line DLm. In the second block BL2, in the reverse order to the first block BL1, the first unit cell UC2,1 is connected to the mth data line DLm, the second unit cell UC2,2 is connected to the m-1 th data line DLm-1 , . . . , the m-1th unit cell UC2, m-1 is connected to the second data line DL2 and the mth unit cell UC2, m is connected to the first data line DL1.
In other words, in the odd blocks BL1 , BL3 . . . , and BL37, the data lines DL1-DLm are in sequence connected to the unit cells UC1-UCm, respectively, and, in the even blocks BL2, BL4, . . . , and BL38, the data lines DL1-DLm are connected to the unit cells UC1-UCm, in the reverse order. For this reason, first and second reading-out circuits RC1 and RC2 are connected, respectively, to the data lines DL1-DL38 of the odd and even blocks BL1, BL3, . . . , and BL37 and BL2, BL4 . . . , and BL38, in order to read-out the data therefrom, respectively. In result, the data from the odd blocks BL1, BL3, . . . , and BL37 are read out by the first reading-out circuit RC1 and the data from the even blocks BL2, BL4, . . . , and BL38 are read out by the second reading-out circuit RC2. This enables the process of accurate data.
However, the linear contact image sensor of the meander line manner in FIG. 3 is desirable in that there can be prevented the generation of the parasitic capacitances due to the cross-overs between the adjacent data lines DL, but has a disadvantage, in that there are still present the parasitic capacitances due to the cross-overs (portions e in FIG. 3) between the adjacent data and gate address lines DL and GAL. This results in generation of a noise in the data signal and, thus, an unnecessary increase in the data read-out time. There are also present parasitic capacitances due to crossovers (portions f in FIG. 3) between the adjacent data and photodiode reverse bias application lines DL and PBL. These parasitic capacitances absorb a portion of the data signal charges being transmitted through the data lines to the reading-out circuits, resulting in an inaccuracy in the output data and generation of a noise therein.
On the other hand, there may be present parasitic capacitances due to cross-overs (portions g in FIG. 3, between the adjacent gate address and photodiode reverse bias application lines GAL and PBL. These parasitic capacitances are of no direct relevance to the data lines DL, similarly to those due to the cross-overs between the adjacent gate address lines GAL, and thus have no effect on the data signal so far as a short fail is not generated.
The linear contact image sensor of the meander line manner has a particular disadvantage, in that the photodiodes arranged at a constant pitch on a semi-conductor substrate are reduced in size since the data lines DL1-DL38 are passed between the unit cells. This results in a reduction in a light receiving area corresponding to an effective area of the image sensor. For this reason, the meander line manner not only degrades the quality of the image sensor, but it is not applicable to a high resolution image sensor.